While they _____(discuss) how to prevent accidents,another accident ahappened.填were discuss,为什么?前面有while,为什么不加ing?

While they _____(discuss) how to prevent accidents,another accident ahappened.填were discuss,为什么?前面有while,为什么不加ing?
While they _____(discuss) how to prevent accidents,another accident ahappened.
填were discuss,为什么?前面有while,为什么不加ing?

While they _____(discuss) how to prevent accidents,another accident ahappened.填were discuss,为什么?前面有while,为什么不加ing?
应该是WERE DISCUSSING吧,可能答案给错了.